\begin{tabular}{cccc}
	A                                 &
	B                                 & C
	                                  & D            \\
	AAA                               & BBB  & CCC
	                                  & DDD          \\
	\multicolumn{2}{c}{first heading} &
	\multicolumn{2}{c}{second heading}               \\
	one                               & two  & three
	                                  & four         \\
	five                              &      & six
	                                  &              \\
	seven                             &              \\
\end{tabular}
